JPWO2013146514A1 - Manufacturing method of inorganic fiber bonded ceramics - Google Patents

Abstract

A method for producing an inorganic fiber-bonded ceramic that can produce an inorganic fiber-bonded ceramic with few defects and an equivalent structure and mechanical properties at the end and the center with high yield and can be increased in size provide. A laminate in which a molded body of coated inorganic fibers composed of an inorganic fiber portion made of inorganic fibers having a thermal decomposition start temperature of 1900 ° C. or less and a surface layer made of an inorganic substance for bonding the inorganic fibers together is laminated. A first press step of setting the carbon die so as to be surrounded by ceramic powder, and pressing in an inert gas atmosphere at a temperature of 1000 to 1800 ° C. and a pressure of 5 to 50 MPa, and the ceramic obtained in the first press step A second pressing step of pressing the coated laminate in an inert gas atmosphere at a temperature of 1600 to 1900 ° C. and at a temperature higher than that of the first pressing step and a pressure of 5 to 100 MPa. The present invention relates to a method for producing fiber-bonded ceramics.

Description

  INDUSTRIAL APPLICABILITY The present invention can produce an inorganic fiber-bonded ceramic having few defects and having the same structure and mechanical properties at the end and the center with a high yield, and can be increased in size. It relates to the manufacturing method.

  In recent years, in the aerospace field and the environment / energy field, in order to increase efficiency and energy, a highly reliable material having excellent heat resistance and high thermal insulation and mechanical properties is desired. It is rare. One of the candidate materials is inorganic fiber bonded ceramics. Inorganic fiber-bonded ceramics are insensitive to defects and have high fracture resistance compared to single ceramics. Further, this inorganic fiber-bonded ceramic is very dense compared to ceramic fiber reinforced ceramic matrix composite material (CMC) manufactured by chemical osmosis gas phase method (CVI method) or polymer impregnation method (PIP method). And high surface smoothness can be obtained by machining.

Such inorganic fiber-bonded ceramics are disclosed in Patent Document 1, for example. In summary, the inorganic fiber bonded ceramic described in Patent Document 1 is mainly composed of Si—M—C—O (M represents Ti or Zr) covered with a surface layer mainly composed of SiO ₂ . Obtained by hot-pressing a laminate of ceramic fibers under high-temperature pressurization, and in the hot-pressing process, part of C in the Si-M-C-O fiber is formed on the fiber surface, M in the M—C—O fiber reacts with C and has a structure in which fine particles made of MC are dispersed in an inorganic substance. Therefore, the structure of the inorganic fiber-bonded ceramics is built up in the hot pressing process under high temperature and pressure by utilizing the thermal decomposition reaction of the raw fiber. In other words, in order to obtain a good inorganic fiber-bonded ceramic structure, it is necessary to strictly control the thermal decomposition reaction in the hot pressing process.

JP-A-9-52776

  As described above, inorganic fiber-bonded ceramics are materials that have excellent heat resistance and have both high heat insulation and mechanical properties, but in terms of the need to strictly control the thermal decomposition reaction. Has the following problems.

  (1) When the carbon die used in the hot press process is used several times, a gap is formed on the mating surface between the dies, the dimensional accuracy of the gap between the dies is deteriorated, and the pyrolysis gas is released from the gap between the dies. The amount increases. For this reason, the end of the material close to the carbon die does not have the original structure of the inorganic fiber-bonded ceramic, and high mechanical properties cannot be obtained.

  (2) If the outer dimensions of the laminate of the coated inorganic fiber are not accurately formed, the end of the material close to the carbon die does not have the original structure of the inorganic fiber-bonded ceramic, as in (1) above. High mechanical properties cannot be obtained, and further, the mechanical properties of the entire material are deteriorated. Therefore, it is necessary to produce a laminate with high dimensional accuracy, which takes time.

  (3) In order to increase the size of the inorganic fiber-bonded ceramics, the size of the laminate must be increased, the load on the punch bar and the carbon die increases, and sudden die or upper and lower punch bars The frequency of damage increases.

  (4) If the inorganic fiber-bonded ceramic is increased in size, the structure will be uneven due to the difference in the amount of pyrolysis gas released between the end and the center of the laminate.

  In this way, stable quality inorganic fiber-bonded ceramics with the same structure and mechanical properties at the end and center can be controlled precisely by controlling the thermal decomposition reaction in the hot pressing process, reducing yield and cost. In order to manufacture and to promote the enlargement of inorganic fiber-bonded ceramics, the conventional methods for manufacturing inorganic fiber-bonded ceramics are not necessarily sufficient.

  The present invention has been made in view of the above problems, and can produce inorganic fiber-bonded ceramics with a low yield and with a high yield in an inorganic fiber-bonded ceramic having the same structure and mechanical properties at the end and the center. An object of the present invention is to provide a method for producing an inorganic fiber-bonded ceramic that can be increased in size.

  In order to achieve the above object, the present inventors have conducted extensive research. As a result, the ceramic powder is placed around the laminate and hot-pressed in two stages. During the pressing of the eye, the ceramic powder is hermetically sealed in advance so that the release of pyrolysis gas of the inorganic fiber can be suppressed. By making uniform, it is possible to produce inorganic fiber bonded ceramics with few defects and having the same structure and mechanical properties at the end and the center with good yield, and it is also possible to increase the size. I found it.

  That is, the present invention relates to a molded body of coated inorganic fiber comprising an inorganic fiber portion made of inorganic fibers having a thermal decomposition start temperature of 1900 ° C. or less and a surface layer made of an inorganic substance for bonding the inorganic fibers together. A first pressing step in which a laminate obtained by laminating a laminate is set on a carbon die so as to be surrounded by ceramic powder, and pressed in an inert gas atmosphere at a temperature of 1000 to 1800 ° C. and a pressure of 5 to 50 MPa, and the first press A second pressing step of pressing the ceramic-coated laminate obtained in the step in an inert gas atmosphere at a temperature of 1600 to 1900 ° C. and at a temperature higher than the first pressing step and a pressure of 5 to 100 MPa. A method for producing an inorganic fiber-bonded ceramic is provided.

In the method for producing an inorganic fiber-bonded ceramic of the present invention, the inorganic fiber part is (a) an amorphous substance containing Si, M, C, and O (M represents Ti or Zr), (b) β. An aggregate of crystalline ultrafine particles containing SiC, MC and C and an amorphous material containing SiO ₂ and MO ₂ (M is the same as (a)), or (c) (a) above And (b) an amorphous substance (M represents Ti or Zr), (d) Si and O, and optionally M. e) a crystalline substance containing crystalline SiO ₂ and / or MO ₂ (M is the same as (d)), or (f) an inorganic substance containing a mixture of (d) and (e) above. It can consist of substances.

  In the method for producing an inorganic fiber-bonded ceramic of the present invention, the thickness T (unit: μm) of the surface layer is T = aD (where a is a numerical value in the range of 0.023 to 0.090. , D is the diameter (unit: μm) of the coated inorganic fiber.

  In the method for producing an inorganic fiber-bonded ceramic of the present invention, the ceramic powder can be an alumina powder.

In the method for producing an inorganic fiber-bonded ceramic of the present invention, the ceramic powder is a mixture of an inorganic substance that melts at 1800 ° C. or less and an inorganic substance that has a melting temperature higher than the pressing temperature in the second pressing step. The inorganic substance that melts at 1800 ° C. or less can be made of glass mainly composed of SiO ₂ , and the inorganic substance that has a melting temperature higher than the pressing temperature of the second pressing step can be carbon or BN. . Moreover, the atmospheric pressure of said 1st press process and a 2nd press process can be 0.01-1 Mpa.

  As described above, according to the present invention, inorganic fiber-bonded ceramics having few defects and having the same structure and mechanical properties at the end portion and the central portion can be manufactured with high yield, and the size can be increased. A method for producing a possible inorganic fiber-bonded ceramic can be provided.

(A) Top view of a die composed of four parts used in this example, (b) A perspective view of one part after the die is divided, and (c) (b) is an enlarged photograph of a dotted line part. FIG. 4 is a schematic view showing a photograph showing a representative die in which the inner surface is damaged due to the influence of gas generated by thermal decomposition and the position of the photographed die. (A) The conceptual diagram which has arrange | positioned the laminated body enclosed with ceramic powder in the die | dye, (b) The conceptual diagram which has arrange | positioned the laminated body without using ceramic powder in the die | dye. It is a photograph which shows the visual observation result after the fluorescence flaw test of the inorganic fiber bond-type ceramics obtained in Examples 1, 2 and Comparative Examples 1, 2. It is a figure which shows the change of the 4-point bending strength from the edge part of the inorganic fiber bond type | mold ceramics obtained in Example 1, 2 and Comparative Example 1, 2 to the center part. It is a photograph which shows the result of having observed the test piece side surface after the bending test of the inorganic fiber bond-type ceramics obtained in Example 2 and Comparative Example 2 with the electron microscope. It is a figure which shows the change of the 4-point bending strength of the edge part and center part of the inorganic fiber bond type ceramics obtained in Example 3. FIG.

Below, suitable embodiment is described in detail about the manufacturing method of the inorganic fiber bond-type ceramics of this invention.
The inorganic fiber-bonded ceramic manufacturing method according to the present embodiment includes a first press step of setting and pressing a laminate as a raw material on a carbon die so as to surround the ceramic powder, and pressing at a temperature higher than the first press step. A second pressing step.

  In the present embodiment, the laminate as a raw material of the inorganic fiber-bonded ceramic is composed of an inorganic fiber portion made of inorganic fibers having a thermal decomposition start temperature of 1900 ° C. or less and a surface made of an inorganic substance for bonding the inorganic fibers together. It can obtain by laminating | stacking the molded object of the covering inorganic fiber comprised by a layer. There is no special restriction | limiting about the form of the molded object of a coating inorganic fiber, It can be a continuous fiber, the chopped short fiber which cut | disconnected the continuous fiber, or the sheet-like thing or textile fabric which arranged the continuous fiber in one direction.

In the present embodiment, the molded body of the coated inorganic fiber is obtained by heating the following inorganic fiber to a temperature in the range of 500 to 1600 ° C. in an oxidizing atmosphere, for example, according to the method described in JP-A No. 62-289441. Thus, it can be prepared so as to be constituted by an inorganic fiber portion made of inorganic fibers having a thermal decomposition starting temperature of 1900 ° C. or less and a surface layer made of an inorganic substance for bonding the inorganic fibers. The inorganic fiber used as a raw material for the molded body of the coated inorganic fiber is a fibrous material composed of an inorganic substance, and examples thereof include Si ₃ N ₄ type and SiC type, but particularly excellent in high temperature strength. SiC fiber is preferred. As SiC fiber, commercially available SiC ceramic fiber can be used, and typical ones include Tyranno fiber (registered trademark) sold by Ube Industries, or Nippon Carbon. Examples include Nicalon (registered trademark) fiber sold by Co., Ltd. In particular, Tyranno Fiber (registered trademark) sold by Ube Industries, Ltd. is preferable.

The molded body of the coated inorganic fiber is composed of an internal inorganic fiber portion and a surface layer outside the inorganic fiber portion. The inorganic fiber part includes (a) an amorphous material containing Si, M, C, and O (M represents Ti or Zr. The same applies hereinafter), (b) contains β-SiC, MC, and C. An assembly of crystalline ultrafine particles and an amorphous material containing SiO ₂ and MO ₂ , or (c) an inorganic material containing a mixture of (a) and (b) above, the surface layer being (D) an amorphous material containing Si and O, optionally M, (e) a crystalline material containing crystalline SiO ₂ and / or MO ₂ , or (f) (d) and (e) above It is preferable that it is comprised with the inorganic substance containing a mixture with these. The ratio of each element of the inorganic fiber constituting the inorganic fiber portion is usually Si: 30-60% by mass, M: 0.5-35% by mass, preferably 1-10% by mass, C: 25-40% by mass. , O: 0.01 to 30% by mass is preferable. The equivalent diameter of the coated inorganic fiber is not particularly limited, but is preferably 5 to 20 μm. The surface layer of the coated inorganic fiber is preferably mainly composed of SiO ₂ .

  Further, by changing the thickness of the surface layer of the coated inorganic fiber according to the fiber diameter of the inorganic fiber portion (diameter of the inorganic fiber), it becomes possible to further stabilize the characteristics of the inorganic fiber-bonded ceramic. When the fiber diameter is D μm, the thickness T μm of the surface layer is preferably in the range of 0.023D to 0.090D. When the thickness of the surface layer becomes thinner than 0.023D, the effect of suppressing thermal decomposition of inorganic fibers by the surface layer tends to be small. On the other hand, if the thickness of the surface layer is greater than 0.090D, the proportion of the inorganic fiber portion of the coated inorganic fiber in the fiber-bonded ceramic decreases, and the high-temperature characteristics tend to deteriorate.

  In the method for producing an inorganic fiber-bonded ceramic according to the present embodiment, the laminate obtained as described above is set on a carbon die so as to be surrounded by ceramic powder, and the temperature is 1000 to 1800 ° C. in an inert gas atmosphere. And the first press step of pressing at a pressure of 5 to 50 MPa, and the ceramic-coated laminate obtained in the first press step at a temperature of 1600 to 1900 ° C. in an inert gas atmosphere and from the first press step A second pressing step of pressing at a higher temperature and a pressure of 5 to 100 MPa.

  In the present embodiment, the ceramic powder disposed around the laminate is sealed in advance in the first press step of the first step out of the two steps of hot press so that the release of pyrolysis gas of inorganic fibers can be suppressed in advance. By making it into a state, the thermal decomposition reaction of the inorganic fibers in the second press step of the second stage can be made uniform over the entire molded body.

  Hereinafter, the ceramic powder surrounding the laminate, which is a feature of the present embodiment, will be described. In this embodiment, the ceramic powder is lower than the press temperature of the second press step to the extent that the release of pyrolysis gas of the inorganic fibers can be suppressed in the first press step in order to achieve the structure of the inorganic fiber-bonded ceramic. It is used to cover the laminate by heating at a temperature. Therefore, it is difficult to strictly control the gas in the molded body because the gas generated by the thermal decomposition reaction is released through the voids of the ceramic powder simply by covering with the ceramic powder. In order to strictly control, it is necessary to heat at a temperature lower than the press temperature in the second pressing step so that the hermetically sealed state can be suppressed to prevent the release of pyrolysis gas. The sealed state that can suppress the release of pyrolysis gas does not need to be a sealed state that completely blocks pyrolysis gas, but the sealed state that can maintain the composition that forms the structure of the inorganic fiber-bonded ceramics. preferable. Since the properties such as yield and strength of the inorganic fiber-bonded ceramics change depending on the sealed state, the sealed state may be managed according to the purpose and the degree of requirement.

  In some cases, the gas generated by the thermal decomposition needs to be released out of the die appropriately. If the temperature at which the ceramic powder is sealed can be controlled, release and suppression of the pyrolysis gas can be controlled. For example, when the composition of the inorganic fiber-bonded ceramic is strictly controlled at the raw fiber stage, the temperature at which the ceramic powder is sealed is lowered so as not to release the pyrolysis gas outside the die. Conversely, when it is desired to increase the release of pyrolysis gas, the temperature at which the ceramic powder is sealed is increased. Depending on the state of the thermal decomposition reaction of the inorganic fiber, the kind and composition of the ceramic powder can be changed, and the temperature at which the ceramic powder becomes sealed can be controlled to control the release and suppression of the pyrolysis gas.

  The ceramic powder surrounding the laminate is preferably a ceramic powder that is sintered in the range of 1000 to 1800 ° C. As such a ceramic powder, for example, an alumina powder that is sintered in a range of 1300 to 1500 ° C. to be in a sealed state can be mentioned. Alumina powder is suitably used because it is relatively inexpensive, easily available, and excellent in stability at high temperatures.

The ceramic powder may be a mixture of an inorganic substance that melts at 1800 ° C. or less and an inorganic substance that has a melting temperature higher than the pressing temperature in the second pressing step. Examples of the inorganic substance that melts at 1800 ° C. or lower include quartz glass and aluminosilicate glass. Moreover, carbon, SiC, BN etc. are mentioned as an inorganic substance whose melting temperature is higher than the press temperature of a 2nd press process. In particular, the inorganic material that melts at 1800 ° C. or less is glass mainly composed of SiO ₂ , and the inorganic material whose melting temperature is higher than the pressing temperature in the second pressing step is BN. By using a mixture of glass and BN powder mainly composed of SiO ₂ , the gap of BN powder is sealed by softened or melted SiO ₂ , and the release of pyrolysis gas is suppressed within the range of 1300-1500 ° C. If the laminate is covered with a densified ceramic, the pyrolysis gas can be controlled.

  As described above, one of the points of this embodiment is that, in the first pressing step, the release of the pyrolysis gas is suppressed by heating the laminate in which the ceramic powder is arranged around the pressing temperature of the second pressing step. The periphery of the laminate is sealed with ceramics as much as possible. Thereby, the following three problems can be solved.

  The first problem is the life of the carbon die. As described above, in general, inorganic fiber-bonded ceramics achieve a fine and complicated structure by controlling the thermal decomposition of raw fiber during the hot pressing. In the hot pressing process, the composition of the raw fiber is controlled while releasing the gas (SiO, CO, etc.) derived from the elements constituting the fiber generated by the thermal decomposition reaction through the gap between the dies. Yes. At this time, carbides and oxides mainly containing Si are generated on the surface of the carbon die by the reaction between the carbon die and the released gas. Therefore, when the carbon die is used several times, the generated carbides and the like are accumulated, and a gap is formed on the mating surface between the dies. Further, if this carbide or the like is removed, a part of the carbon die is chipped together with the carbide or the like, and a gap is similarly formed on the mating surface between the dies. If this happens, the dimensional accuracy of the gap between the dies will deteriorate, the amount of pyrolysis gas released from the gap between the dies will increase, and the edge of the material close to the carbon die will have the original structure of inorganic fiber bonded ceramics. Therefore, high mechanical properties cannot be obtained. Furthermore, if the dimensional accuracy is deteriorated, the mechanical properties of the entire material may be deteriorated. Therefore, the carbon die needs to be frequently replaced although it varies depending on the hot press conditions. For this reason, since the cost of the dice increases, it is necessary to reduce the cost of the dice.

  Secondly, even if the dimensional accuracy of the die is kept constant, if the outer dimensions of the laminate of the coated inorganic fiber are not accurately formed, the heat from the gap between the die and the laminate is caused by the variation of the gap between the die and the laminate. The problem is that the amount of cracked gas released becomes non-uniform and the thermal decomposition reaction cannot be strictly controlled. However, since the coated inorganic fiber is very poor in workability, there is a variation in the cutting size, and when this variation becomes large, the end of the material close to the carbon die does not have the original structure of the inorganic fiber-bonded ceramic, High mechanical properties cannot be obtained. Furthermore, if the dimensional accuracy is deteriorated, the mechanical properties of the entire material may be deteriorated. Therefore, it is necessary to produce a laminate with high dimensional accuracy, which takes time.

  Furthermore, as a third problem, there is a non-uniform structure due to the difference in the amount of pyrolysis gas released at the end and the center of the laminate as the inorganic fiber bonded ceramic material becomes larger. As described in the first issue, inorganic fiber-bonded ceramics release gas (SiO, CO, etc.) derived from the elements constituting the fibers generated by the thermal decomposition reaction during the hot pressing process from the gap between the dies. The fine structure is achieved by controlling the composition in the raw material fiber. For this reason, when the size of the inorganic fiber-bonded ceramics is increased, the structure is unsatisfactory due to the difference in holding time at the target temperature and the ease of release of pyrolysis gas at the end and center of the green body. It becomes uniform. For example, when the molding temperature is set to 1800 ° C. and the holding time is set to 1 hour, the end portion of the molded body reaches the target temperature earlier than the center portion. In some cases, a temperature difference may occur between the end and the center. If it does so, the timing and quantity which generate | occur | produce pyrolysis gas differ with the difference of the shaping | molding temperature and holding time in an edge part and a center part. In order to increase the size of the molded body of the inorganic fiber-bonded ceramics, it is necessary to make the generation and release amount of pyrolysis gas at the end and the center of the molded body uniform.

  According to the present embodiment, in the first pressing step, the ceramic powder is previously sealed in a state that can suppress the release of pyrolytic gas of the inorganic fiber, thereby forming the thermal decomposition reaction of the inorganic fiber in the second pressing step. By making it uniform over the entire area, the above three problems can be solved, and the inorganic fiber-bonded ceramics having the same structure and mechanical properties at the end portion and the central portion can be produced with a high yield. It is also possible to increase the size.

  The ceramic powder is preferably a fluid powder. Thereby, the following fourth problem can be solved at the same time.

  The fourth is a sudden die or breakage of the upper and lower punch bars. It is very difficult to make uniform the fiber volume ratio, which is the volume ratio of fibers per unit volume of the raw fiber laminate before hot pressing, and the laminate is partially dense. For this reason, a non-uniform load is applied to the laminate during pressurization of the hot press. If it does so, compared with the position where the fiber volume ratio of a laminated body is low, the load beyond a plan will be applied to the position where a fiber volume ratio is high. This uneven load may cause the carbon die to break suddenly. Furthermore, the impact is propagated to the upper and lower punch bars made of carbon, and the punch bars may be damaged. These sudden dice and punch bar breakage may damage the heater and insulation of the hot press apparatus. This sudden breakage is expected to occur more frequently as the size of the laminate increases and the load on the punch bar and carbon die increases. In order to prevent this sudden die damage and propagation of impact to the upper and lower punches, a tough ceramic composite material or a carbon fiber reinforced carbon composite material (CC composite material) is sandwiched between the laminate and the die. It is effective, but this alone is not a fundamental solution. In the future, in order to increase the molding size of inorganic fiber-bonded ceramics, it is necessary to prevent this sudden damage.

  In this embodiment, by using a fluid powder as the ceramic powder, it is possible to reduce the density of the fiber volume ratio of the laminate. It is possible to prevent the carbon die from being suddenly damaged due to concentration of load. In order to increase the fluidity of the ceramic powder, for example, it is also effective to use the powder after making it spherical with a spray dryer or the like.

  Next, the press in the first press process and the second press process will be specifically described. First, a laminate covered with ceramic powder is placed in a carbon die used for pressing, a pressing punch bar is set thereon, and the resultant is put into a hot press apparatus. At this time, in order to improve the releasability between the carbon die and the ceramic powder, BN may be sprayed onto the carbon die. In addition, sandwiching the carbon sheet between the carbon die and the ceramic powder is also an effective means for improving the releasability. Similarly, regarding the releasability between the ceramic powder and the laminate, by sandwiching the carbon sheet between the ceramic powder and the laminate, it is possible to easily take out the inorganic fiber-bonded ceramic compact after hot press molding.

  After setting the dice in the hot press machine, replace with an inert atmosphere. Then, the laminate is covered with the ceramics in which the ceramic powder is densified, and the temperature is raised to the set temperature of the first press step in the range of 1000 to 1800 ° C. where the release state of the pyrolysis gas from the laminate is suppressed. Warm up. The temperature increase rate at this time is not particularly defined, but a temperature increase rate with a small temperature difference between the outer peripheral portion and the central portion of the laminate is desirable. Moreover, in order to make the temperature of the outer peripheral part and center part of a laminated body uniform, you may set the time of temperature holding before the press below the press temperature of a 1st press process. And the pressure of 5-50 Mpa is loaded in the press temperature of a 1st press process. This press may be in a state where the temperature is maintained or while the temperature is raised. When the press in the first press step is completed, the temperature is continuously raised to a predetermined temperature in the range of 1600 to 1900 ° C. higher than the press temperature in the first press step, a pressure of 5 to 100 MPa is applied, and the press in the second press step It can be performed. As for the rate of temperature increase from the first press step to the second press step, a temperature increase rate at which the temperature difference between the outer peripheral portion and the center portion of the laminate is small is desirable as in the first press step. In order to make the temperature of the outer peripheral part and the central part uniform, the temperature holding time may be set.

  The pressing in the first pressing step and the second pressing step may be performed at intervals or may be performed continuously. However, once the temperature in the first press step is finished, once the temperature is lowered, cracks occur in the ceramics in the sealed state, and from the crack, the inorganic fibers are removed from the crack until the temperature is raised to the press temperature in the second press step. Pyrolysis gas may be released to the outside. Moreover, it is preferable to perform the press process of a 1st press process and a 2nd press process continuously from a viewpoint of efficiency improvement of a press process.

  The atmosphere of the first press step and the second press step is an inert gas atmosphere, and an argon gas atmosphere is generally preferable. It is also effective to increase the atmospheric pressure as a method of further enhancing the effect of controlling the gas generated by thermal decomposition by sintering ceramic powder. Increasing the atmospheric pressure in the hot press apparatus has the effect of reducing the release of gas generated by the thermal decomposition reaction. Further, increasing the atmospheric pressure is an effective means for preventing the release of pyrolysis gas due to the variation in the hermetic state of the ceramic powder. By increasing the atmospheric pressure from the start of temperature rise, thermal decomposition can be suppressed even before the ceramic powder is sintered. The atmospheric pressure is usually in the range of 0.01 to 1 MPa, particularly preferably in the range of 0.1 to 1 MPa. However, in order not to entrap voids in the inorganic fiber-bonded ceramics, it is necessary to be below the pressing pressure.

  Hereinafter, the present invention will be illustrated by examples and comparative examples. First, the inspection and characteristic evaluation of the inorganic fiber bonded ceramics of Examples and Comparative Examples were performed by the following methods.

(Fluorescence testing)
In order to inspect the state of surface defects at the edge and center of the formed inorganic fiber-bonded ceramics, a fluorescent flaw detection test used for inspection of precision machine parts was performed. The method of the fluorescent flaw detection test is as follows. First, after grinding the surface of the formed inorganic fiber-bonded ceramics by about 0.5 to 1 mm with a surface grinder, dirt such as deposits and oils that impede penetration of the permeate is washed with ethanol, and 70 ° C. And dried. Next, brush the penetrant (Super Glow Fluorescent Penetrant, OD-2800 III) and let it stand for about 10 minutes, then lightly wash the penetrant with running water and remove the developer (Super Glow, DN-600P). Sprayed very little. Then, after leaving for about 5 minutes, using an ultraviolet irradiation device having an ultraviolet intensity (800 μW / cm ² or more) with which the indication pattern can be clearly identified, immediately irradiate the surface with ultraviolet rays having a wavelength of 330 to 360 nm in the dark. It was observed visually and photographed.

(4-point bending test)
From the inorganic fiber-bonded ceramics after the second pressing step, a 4-point bending test piece with a width of 4 mm, a height of 3 mm, and a length of 40 mm was taken, and using a material testing machine, the distance between the upper fulcrums was 10 mm and the distance between the lower fulcrums. A 4-point bending test was performed at 30 mm and a crosshead speed of 0.5 mm / min, and the bending strength from the end to the center of the formed inorganic fiber-bonded ceramic was measured.

Example 1
As an inorganic fiber, a cocoon fabric is prepared using a Tyranno fiber (registered trademark: manufactured by Ube Industries, Ltd.) having a fiber diameter of 8.5 μm, cut into 80 × 80 mm square, and then kept in air at 1000 ° C. for 20 hours. Thus, a woven fabric sheet made of coated inorganic fibers composed of an inorganic fiber portion and a surface layer was obtained. A uniform surface layer having an average of about 510 nm corresponding to a = 0.06 was formed on the surface of the coated inorganic fiber. Here, a is a = T / D, where the thickness of the surface layer of the coated inorganic fiber is T μm and the diameter of the inorganic fiber is D μm. And 100 sheets of this insulator fabric sheet were laminated | stacked, and the laminated body hardened with the organic binder was produced. The inorganic fiber portion of the coated inorganic fiber in the laminate is mainly composed of an amorphous substance containing Si, Ti, C and O, and crystalline ultrafine particles containing β-SiC, TiC and C, and SiO ₂ and TiO. _The surface layer was mainly composed of an amorphous material containing Si, O, and Ti.

Next, the produced laminate was set on a carbon die.
In FIG. 1, the photograph of the die | dye used for the press of the 1st press process of a present Example and a 2nd press process is shown. 1 (a) is a top view of a four-part die, FIG. 1 (b) is a perspective view of one part when the die is divided, and FIG. 1 (c) is a perspective view of FIG. 1 (b). It is the photograph which expanded the dotted line part of the perspective view of one part. As shown in FIG. 1A, the dice form one die with four parts, and each of the four parts can be divided. The perspective view of one of the parts is shown in FIG. 1 (b). When the inside of the part is used in a press, the inside of the part is in contact with punch bars, laminates, ceramic powder, etc., and is affected by the gas generated by thermal decomposition. The surface is damaged. A typical damaged die is shown in FIG. The die used in this example is a carbon die having an inside dimension of 90 × 90 mm square, where the surface of the die, which is difficult to produce an inorganic fiber bonded ceramic molded body, is damaged. On the surface inside the die, it was observed that there were irregularities formed by the influence of gas generated by thermal decomposition.

  A method of setting the laminate on the carbon die will be described with reference to FIG. First, the carbon sheet 6 was disposed on the side surface of the carbon die 1 (carbon mold) on which the lower punch bar 10 was set. Next, a 5 mm thick CC composite material spacer 5 is placed on the set lower punch bar 10, a carbon sheet 6 having a thickness of 0.2 mm is laid thereon, and 120 g of alumina powder 8 is placed on the surface. Flattened. Then, a carbon sheet 6 was laid on the alumina powder 8 to arrange the laminate 7. Next, 30 g of alumina powder 8 is filled in the gap between the laminate 7 (80 × 80 mm) and the die 1 (90 × 90 mm), and a carbon sheet 6 is further laid on the laminate 7, and the alumina powder is also deposited thereon. 120 g of 8 was put and the surface was made flat. Thus, the laminate 7 is surrounded by the alumina powder 8. Thereafter, a carbon sheet 6 was laid on the end of the alumina powder 8, a CC composite material spacer 5 was placed thereon, and finally the upper punch bar 4 was set.

  FIG. 2A shows a state in which the laminate is set on the carbon die. 2A is a schematic diagram, and the carbon sheet 6 is emphasized. However, the thickness of the carbon sheet 6 is 0.2 mm, which is further reduced by pressurization, and alumina powder 8 is formed on the surface. Due to the close contact, pyrolysis gas is hardly released from the die between the alumina powder 8 and the carbon sheet 6. In this state, pressing in the first pressing step was performed in an argon atmosphere at a temperature of 1400 ° C. and a pressure of 40 MPa. Subsequently, while maintaining the pressure, the temperature was raised to 1750 ° C. and held for 1 hour to perform pressing in the second pressing step, and an inorganic fiber-bonded ceramic according to Example 1 was obtained.

(Example 2)
Next, the laminate is set on a carbon die in the same procedure as in Example 1, and the first pressing step is performed at a temperature of 1400 ° C. and a pressure of 40 MPa, and then the temperature is increased to 1850 ° C. while maintaining the pressure. By holding for 1 hour, the second pressing step was pressed to obtain an inorganic fiber-bonded ceramic according to Example 2. Other conditions are the same as in the first embodiment. The alumina surrounding the laminate is cracked due to the difference in thermal expansion between the fiber-bonded ceramic and alumina at the cooled room temperature after the second pressing step, and between the alumina powder and the laminate. Since the carbon sheet was sandwiched, it was easily removed by tapping the corners of alumina with a plastic hammer.

  The photograph after the fluorescent flaw test of the obtained inorganic fiber bonded ceramics according to Examples 1 and 2 is shown in FIGS.

  Comparing two inorganic fiber-bonded ceramics, the inorganic fiber-bonded ceramics of Example 1 having a slightly lower molding temperature tend to have fewer defective portions (white portions in the black-and-white photo in FIG. 3). However, all have few defective parts. The white portion in FIG. 3 indicates that voids are present on the side surface of the inorganic fiber bonded ceramic. It is thought that this void was formed because the decomposition gas generated by the thermal decomposition reaction was excessively released out of the die. Although this void will be described later, the side surface of the test piece after the bending test was confirmed by observing with an electron microscope. In the photograph after the fluorescent flaw detection test, the striped pattern observed in the entire inorganic fiber-bonded ceramic is a fiber texture pattern and not a defect.

  Next, FIG. 4 shows the result of a four-point bending test from the end to the center of the inorganic fiber-bonded ceramic. Despite the use of a damaged die, both Examples 1 and 2 maintained stable 4-point bending strength from the end to the center. Moreover, the side surface of the 4-point bending test piece extract | collected from the edge part was observed with the electron microscope. The result is shown in FIG. The gap between the fibers was filled with the surface layer of the raw fiber, and no void was observed. It was found that the inorganic fiber-bonded ceramics of Examples 1 and 2 were equivalent to the center part in the structure and mechanical properties up to the end part. As a result, it became clear that the previously discarded dies could be used, and it was found that the life of the dies could be extended. In addition, a laminate (80 × 80 mm) as small as 10 mm with respect to the dimensions of the die (90 × 90 mm) was used, and the above-mentioned result could be achieved even though the clearance between the die and the laminate was very large. .

(Example 3)
After a cocoon fabric made of Tyranno fiber (registered trademark: manufactured by Ube Industries Co., Ltd.) having a fiber diameter of 8.5 μm was cut into 180 × 180 mm squares, a laminate in which 500 cocoon fabric sheets were laminated in the same manner as in Example 1 Produced. As the carbon die, a large carbon die having a 190 × 190 mm square inner dimension with a damaged die surface, which is difficult to produce an inorganic fiber-bonded ceramic molded body, was used. The method of setting the laminate on the carbon die is the same as in Example 1. However, since alumina powder has a larger gap volume than Example 1, 500 g below the laminate, and the laminate (180 × 180 mm) 80 g was put in a gap between dies (190 × 190 mm), and 500 g was put on the laminate. In this state, pressing in the first pressing step was performed in an argon atmosphere at a temperature of 1400 ° C. and a pressure of 40 MPa. Subsequently, the second press step was pressed under the conditions of a temperature of 1750 ° C. and a holding time of 2 hours while maintaining the pressure, and an inorganic fiber-bonded ceramic according to Example 3 larger than Example 1 was obtained.

  Fifteen bending test specimens were collected in the thickness direction from the end and center of the 180 × 180 mm surface of the obtained inorganic fiber-bonded ceramic according to Example 3 having a thickness of about 180 × 180 × about 60 mm. Then, the four-point bending strength at the end and the center was measured. The measurement results are shown in FIG. Despite the use of a damaged die and a large size compared to Example 1, there is variation in the strength of the end and center of the inorganic fiber bonded ceramic according to Example 3. There wasn't. As a result, it became clear that the previously discarded dies could be used, and it was found that the life of the dies could be extended. In addition, a laminate (180 × 180 mm) as small as 10 mm with respect to the dimensions of the die (190 × 190 mm) was used, and the above-mentioned result could be achieved even though the clearance between the die and the laminate was very large. . Furthermore, compared with Example 1, although it is a big shape and the density of a laminated body is large, there is no breakage of a sudden die etc., and there is no intensity | strength variation in a center part and an edge part, and an inorganic fiber bond type Ceramics could be formed.

(Comparative Example 1)
An insulator woven fabric made of Tyranno fiber (registered trademark: manufactured by Ube Industries Co., Ltd.) having a fiber diameter of 8.5 μm is cut into 89 × 89 mm square, then treated in air at 1000 ° C. for 20 hours, and an inorganic fiber portion and a surface layer A woven sheet of coated inorganic fibers composed of A uniform surface layer having an average of about 510 nm corresponding to a = 0.06 was formed on the surface of the coated inorganic fiber as in the example. Next, similarly to Example 1, hot pressing was performed using a carbon die having a 90 × 90 mm square inside dimension with a damaged die surface, which was difficult to produce an inorganic fiber bonded ceramic molded body. A method of setting the laminate on the die will be described with reference to FIG. First, the carbon sheet 6 was disposed on the side surface of the carbon die 1 (carbon mold) on which the lower punch bar 10 was set. Next, a 5 mm thick CC composite material spacer 5 is placed on the set lower punch bar 10, a carbon sheet 6 having a thickness of 0.2 mm is laid thereon, and 100 woven fabric sheets are laminated to form an organic binder. The laminate 7 hardened in (1) was placed. Then, a carbon sheet 6 was laid thereon, a CC composite material spacer 5 was placed on the carbon sheet 6, and finally the upper punch bar 4 was set. FIG. 2B shows a state where the laminate is set on a carbon die. In the same manner as in Example 1, hot press molding was performed in an argon atmosphere under the conditions of a pressure of 40 MPa, a temperature of 1750 ° C., and a holding time of 1 hour to obtain an inorganic fiber bonded ceramic according to Comparative Example 1.

(Comparative Example 2)
Next, the laminate was set on a carbon die in the same procedure as in Comparative Example 1, and hot press molding was performed at a temperature of 1850 ° C. to obtain an inorganic fiber bonded ceramic according to Comparative Example 2. Other conditions are the same as in Comparative Example 1.

  The photograph after the fluorescence flaw test of the two types of inorganic fiber-bonded ceramics according to Comparative Examples 1 and 2 is shown in FIG. 3 (c) and 3 (d) show the results of Comparative Examples 1 and 2, respectively. (C) Comparative Example 1 having a molding temperature of 1750 ° C. has a portion where the white portion of the black and white photograph reaches the center. This indicates that there are defects (cracks) on the surface. Further, in (d) Comparative Example 2 at a molding temperature of 1850 ° C., the white portion at the end is slightly wider than Comparative Example 1. This indicates that there are many defects (voids existing from the side surface portion to the center portion of the inorganic fiber-bonded ceramic) at the end portion, and the range of the defects increases as the molding temperature rises. Both inorganic fiber-bonded ceramics obtained in Comparative Examples 1 and 2 have cracks in Comparative Example 1 compared to the inorganic fiber-bonded ceramics obtained in Examples 1 and 2, and Comparative Example 2 Then, the defects (voids) at the end portion become wider toward the surface. Next, FIG. 4 shows the results of a four-point bending test from the end to the center of the inorganic fiber-bonded ceramics according to Comparative Examples 1 and 2. Since the damaged dies were used, both Comparative Examples 1 and 2 showed large variations in the four-point bending strength from the end to the center, and all showed lower values than the four-point bending strength of the example. It was. Moreover, the result of having observed the side surface of the 4-point bending test piece extract | collected from the edge part with an electron microscope is shown in FIG.5 (b). Many voids were observed from the edge of the inorganic fiber bonded ceramic. This result was in good agreement with the result of the fluorescence flaw detection test.

  From the above, according to the present invention, even with a damaged die having poor dimensional accuracy, which has been difficult to control the gas generated by the thermal decomposition in the hot press process, there is no void up to the end, and It can also be seen that an inorganic fiber-bonded ceramic that maintains high mechanical properties from the center to the end can be obtained.

  The inorganic fiber-bonded ceramic obtained by the method for producing an inorganic fiber-bonded ceramic of the present invention can be used in a severe environment of high temperature including an oxidizing atmosphere of 1000 ° C. or higher in air and has excellent heat resistance. And has both high heat insulation properties and mechanical properties.

1 Carbon dice (parts)
3 Position for Setting Laminate 4 Upper Punch Bar 5 CC Composite Spacer 6 Carbon Sheet 7 Laminate 8 Alumina Powder 9 CC Composite Mold 10 Lower Punch Bar 12 Void

Claims (7)

A laminate in which a molded body of coated inorganic fibers composed of an inorganic fiber portion made of inorganic fibers having a thermal decomposition start temperature of 1900 ° C. or less and a surface layer made of an inorganic substance for bonding the inorganic fibers together is laminated. A first press step of setting the carbon die so as to surround the ceramic powder, and pressing in an inert gas atmosphere at a temperature of 1000 to 1800 ° C. and a pressure of 5 to 50 MPa, and the ceramic obtained by the first press step A second pressing step of pressing the coating laminate in an inert gas atmosphere at a temperature of 1600 to 1900 ° C. and at a temperature higher than that of the first pressing step and a pressure of 5 to 100 MPa;
A method for producing an inorganic fiber-bonded ceramic, comprising: The inorganic fiber part is
(A) an amorphous material containing Si, M, C and O (M represents Ti or Zr),
(B) an assembly of crystalline ultrafine particles containing β-SiC, MC and C and an amorphous material containing SiO ₂ and MO ₂ (M is the same as (a)), or (c) It is composed of an inorganic substance containing a mixture of (a) and (b) above,
The surface layer is
(D) Amorphous material containing Si and O, optionally M (M represents Ti or Zr),
(E) a crystalline substance containing crystalline SiO ₂ and / or MO ₂ (M is the same as (d)), or (f) containing a mixture of (d) and (e) above. 2. The method for producing an inorganic fiber-bonded ceramic according to claim 1, wherein the method is made of an inorganic substance.   The thickness T (unit: μm) of the surface layer is T = aD (where a is a numerical value within the range of 0.023 to 0.090, and D is the fiber diameter (unit: μm) of the inorganic fiber portion. 3. The method for producing an inorganic fiber-bonded ceramic according to claim 1 or 2, wherein:   2. The method for producing an inorganic fiber bonded ceramic according to claim 1, wherein the ceramic powder is an alumina powder.   2. The inorganic fiber-bonded ceramic according to claim 1, wherein the ceramic powder includes a mixture of an inorganic substance that melts at 1800 ° C. or less and an inorganic substance that has a melting temperature higher than the pressing temperature of the second pressing step. Manufacturing method. The inorganic substance that melts at 1800 ° C. or less is glass mainly composed of SiO ₂ , and the inorganic substance having a melting temperature higher than the pressing temperature in the second pressing step is carbon or BN. Item 6. A method for producing an inorganic fiber-bonded ceramic according to Item 5. The method for producing an inorganic fiber-bonded ceramic according to claim 1, wherein the atmospheric pressure in the first press step and the second press step is 0.01 to 1 MPa.